[SciPy-User] Notification when array is modified
Christian K.
ckkart@hoc....
Mon Aug 20 19:44:43 CDT 2012
For that purpose I use a subclass of ndarray. See the attached sample.
Hope it helps.
Christian
Am 20.08.12 04:00, schrieb John Jumper:
> I am looking for a method so that I can be notified when the contents
> of a numpy array change.
>
> A simplified class that illustrates the desired functionality is below.
>
> class ComputeDerived(object):
> def __init__(self, n):
> self.A = np.zeros(n)
> self.B = np.zeros(n)
> self.change_mask = np.ones(n, dtype=np.bool)
> self._Derived = expensive(self.A,self.B)
>
> def set_A(self, i, x):
> self.A[i] = x
> self.change_mask[i] = True
>
> def set_B(self, i, x):
> self.B[i] = x
> self.change_mask[i] = True
>
> def Derived(self):
> if np.any(self.change_mask):
> for i in np.nonzero(self.change_mask)[0]:
> self._Derived[i] = expensive(A[i],B[i])
> self.change_mask[:] = False
> return self._Derived
>
> This class works, but I lack the power of numpy's indexing syntax to
> change A or B. I would like to be able to write
> compute_derived.A[(3,5,6)] = 1 and then be notified that A has
> changed. Otherwise, if I want to use a numpy interface for A and B, I
> would have to store old copies of A and B and traverse these copies
> every time Derived is called.
>
> Is there any interface in numpy so that I could expose A and B
> directly as writeable numpy arrays but be notified when they are
> modified? Alternatively, if I subclass ndarray, is there some
> exhaustive list of methods that can change the underlying data (I
> would be worried about view objects here)?
>
> In case it makes a difference, my actual use case is a C++ class
> wrapped using Boost::Python. The numpy arrays A and B would point at
> aligned float* members of my C++ class.
>
> Thank you,
> John Jumper
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: callback_array.py
Type: text/x-python-script
Size: 1357 bytes
Desc: not available
Url : http://mail.scipy.org/pipermail/scipy-user/attachments/20120820/db989794/attachment.bin
More information about the SciPy-User
mailing list